I'm gonna do all of them:
Weedle line vs. Caterpie line: Weedle, definitely. Why have a pretty butterfly when you can have a badass wasp? +1 Black
Shroomish line vs. Paras line: Shroomish. IT HAS POISON HEAL. +1 Black
Misdreavus vs Murkrow: Hard choice, but I choose Murkrow, since I had a Honchkorw on my Diamond team. +1 Black
Houndoom vs. Mightyena: Houndoom. Helhounds > plain wolf-hyena things. +1 Black
Pusle vs. Minun: completely neutral. +0 both
Volbeat vs. Illuminise: also completely neutral. +0 both
Churine line vs. Monmen line: Churine. The final evolution actually looks kind of pretty, at least to me. +1 White
Yuniran line vs. Gothimu line: Yuniran. Gothimu creeps me out. +1 White
Washibon line vs. Baruchai line: Baruchai. Wargle is cool and all, but this is the first time we've had actual vultures. +1 Black
Tornelos vs. Voltolos: Tornelos. It's pure Flying! (Though my favorite of that trio is Landlos.) +1 Black
Reshiram vs. Zekrom: Zekrom. I'm really glad we finally have a Fire/Dragon, but Electric/Dragon is even cooler. Plus, it just looks better. +1 White
More Triple Battles vs. more Rotation Battles: Triple Battles. Rotation Battles sound a bit too complex for me. +1 White
Iris vs. Shaga: Iris. Where the heck is Shaga's mouth? Plus Iris is cute, in a little girl kind of way. +1 White
Black City vs. White Forest: No contest. White Forest you can get the items for free (though in more limited amounts) but the real clincher is that you can actually catch the Pokemon in White Forest. +1 White
And the grand total is...
Black 6, White 6
I guess I'll have White as may main version, since that's what I originally planned to do, and it fits into the "pattern" I've developed over the years playing these games.
Plus, White Forest should be worth multiple points due to all the exclusive Pokemon.